Micrometer (micron) is a metric unit of measurement denoting one millionth of a meter. To give you some idea of how fine a micron is, consider that the smallest particle visible to the unaided human eye is about forty microns (you can see smaller particles through light diffraction).
There are a few rules to remember when sizing a filtration system:
With in-depth cartridge filters, the slower the flow, the more efficient the cartridge is and the longer the user can go between change-outs. At Filters.com, we typically size housings to start out with a clean differential pressure of two pounds or less. You will find that many people in the filter business will quote housings that are undersized for an application so that they quote the lowest capital equipment cost.
The differential pressure (pressure drop) across both the cartridge and housing must be considered cumulatively. The pressure drop across the housing differs from housing to housing, but in most cases, it can be obtained from the housing manufacturer.
Assuming a cartridge vessel is designed for cartridges with a one-inch inside diameter, keep in mind that the flow through the bottom of each filter should not exceed 15-25 gallons per minute (for membrane pre-filters, try not to exceed 15 gpm). These flow rates should not be exceeded because turbulent flow is created on the interior core of the filter, which frequently cause unloading of contaminant from the filter media.
Always consider the viscosity of the material to be filtered when sizing filters or vessels. Also keep in mind that the viscosity of most materials varies depending on temperature. If you have an application where the customer does not want to go over a certain differential pressure and the temperature of the product can go through a wide swing, be careful to find out what the viscosity of the liquid is at both extremes of temperature.
Media migration is the phenomenon in which a portion of the filter (media) itself comes loose from the filter and travels downstream with the liquid or gas being filtered.
An example of this is a piece of fiber from a string-wound filter being carried downstream in the liquid being filtered. Most commodity-type filters, as well as many more sophisticated membrane or membrane pre-filters, experience media migration of some kind or another. To minimize this migration of media, more sophisticated filters are frequently pre-flushed with filtered, deionized or RO (reverse osmosis) water. Typically, a pre-flushing procedure like this removes most of the loose media present in a filter.
With commodity filters, the detrimental effects of media migration can be minimized by re-circulating the material being filtered for several minutes. By doing this, any media that migrates downstream is redirected on the exterior surface of the filter, which filters the media, which has migrated.
“Membranes are selectively permeable barriers that can provide a filter for a range of processes, from removing salt from sea water in desalination plants, to filtering the blood of kidney patients in dialysis machines. Filtration processes using membranes could potentially reduce energy consumption compared to other separation methods.
The membrane is very thin, yet extremely strong
However, many industries use evaporation and distillation techniques rather than membranes, because membranes can be costly to scale up and they are not resistant to the organic solvents used in many industrial refining and chemical processes.
Now, researchers from Imperial College London have developed a prototype crumpled membrane that has the potential to be used widely across industry. The prototype is extremely thin – it would take a stack of ten thousand membranes to match the diameter of a human hair – making it very permeable. It is also strong, and is able to filter organic liquids at pressures of around 50 bar, which is the equivalent to the pressure at around 500 metres below the ocean’s surface. The membrane is durable and resistant in a range of organic solvents.
In a study detailed in the journal Science, the team created a membrane with nanoscale crumples and established that this provides an increased surface area for filtering substances that remains strong and does not buckle, even under extreme pressures. The prototype is 80 millimetres in diameter, but the team is confident that it can be scaled up to industrial areas.
Ultimately, the researchers believe that their prototype membrane could be used to improve or completely replace industrial processes that process organic solvents, which currently rely on evaporation and distillation techniques. Approximately 30 per cent of the world’s energy is currently used by industry, with a substantial fraction of that being used in evaporation and distillation processes. These industries could potentially make major energy savings if they used the membranes, with consequent reductions in carbon dioxide emissions.
Professor Andrew Livingston, co-author of the study from the Department of Chemical Engineering at Imperial College London, said: “Membranes are currently used for a range of important tasks such as making water drinkable and life-saving kidney filtering. The drawback has been that industry hasn’t been able to use membranes in organic liquid systems more widely because they’ve had cost and design limitations. Our research suggests that we can overcome these challenges, which could make these membranes useful for industries ranging from pharmaceutical companies to oil refining. The energy and environmental benefits could be massive.”
Dr Santanu Karan, co-author also from the Department of Chemical Engineering at Imperial College London, added: “I am really excited about this research breakthrough. We now want to work even more closely with industry to further refine our membranes so that they can meet their needs. We hope our work will lead to new collaborations and ultimately, improvements in the way industries use separation processes.”
To test the effectiveness of the membrane in the lab, they team mixed together a solution containing a solvent, alcohol, and dyed molecules of different colours and sizes. They then made the solution percolate through the membrane at high pressures, using a device called a dead-end cell, to see if they could filter out everything apart from the alcohol. The team observed the process using an absorption spectroscopy device, which uses light at different wavelengths to determine what molecules are passing through the membrane. They determined that the membrane was completely effective, with only the alcohol passing through.
The researchers then compared the crumpled membrane to a conventional membrane, carrying out the same experiment. Their aim was to determine how fast their membrane could purify and concentrate the solution compared to the conventional model. They found that the crumpled membrane could separate substances 400 times faster than the conventional membrane.
The team is now planning to further develop and optimise the membrane technology so that it can be scaled up for use in industries such as pharmaceuticals, manufacturing and oil refining.
The research was funded by the Engineering and Physical Sciences Research Council (EPSRC) and the BP International Centre for Advanced Materials.”